Specific binding sites for spin labeled analogues of fatty acyl-CoA (6- and 16-doxylstearoyl-CoA) have been demonstrated on citrate synthase (Caggiano and Powell, J. Biol. Chem. 254 (1979) 2800-2806). We are now preparing photoaffinity labeled fatty acyl-CoA analogues prepared by the methods of Lau, Haley and Barden, Biochem. Biophys. Res. commun. 76 (1977) 843-849. The interactions of these analogues with citrate synthase and malate dehydrogenase will be characterized using activity measurements, radiotracers, and by competitive binding studies using the spin labeled anlogues. The goal of these studies is to determine the location of the fatty acyl-CoA binding site within the primary structure of the enzyme and relate that to the crystal structures which should be available soon. Studies are also in progress of the micelle structure of fatty acyl-Coa and the naure of its association with enzymes.